The present invention relates to a formulation and method for treating wetted surface elements in climate control systems and more particularly, to an improved treatment method and product which arranges long-term effectiveness in climate control systems.
Air-conditioners, heat pumps, dehumidifiers, and humidifiers, can collectively be called climate control systems. All of these systems possess a wetted surface element (xe2x80x9cWSExe2x80x9d) by which or through which air passes. Air-conditioners, heat pumps, and dehumidifiers circulate air by a cooled surface. As the warm air is cooled below its dewpoint, water condenses and accumulates on the cooled surface and typically falls into a collection reservoir where eventually the collected water drains to the outdoors via a drain line. On the wet and cool condensing surface and the collection reservoir, conditions are favorable for the growth of microbes which can be entrained by the passing air. Depending on the operation or duty cycle of the particular system, this condensed water sometimes remains stagnant for long time periods, thereby promoting microbial and fungal growths on water-contacted parts and surfaces.
During winter months, humidifiers are sometimes used to humidify dry air by passing the dry air across a wetted surface. Systems such as pan humidifiers, portable humidifiers, power wetted-element humidifiers, atomizing humidifiers, ultrasonic humidifiers, and rigid media humidifiers are widely used. A humidifier by nature requires a water source and an associated wetted surface which is evaporated into drier air. These water sources can promote microbial and fungal colony growths that could be entrained into the ventilation system via the passing air flow. Treating the water used in these systems with biocides can dramatically reduce the likelihood that airborne toxins are entrained.
The dispersion of microbes such as bacteria, virus, mold, and fungus can be the source of sickness to exposed occupants in the climate controlled area. For example, Legionella pneumophilia has been found to exist in such an environment and has been linked to Legionnaire""s disease. Other microbes can contribute to xe2x80x9csick homexe2x80x9d or xe2x80x9csick buildingxe2x80x9d syndrome. Many people are also allergic to the molds and fungus entrained in the dwelling""s ventilation as the air passes over contaminated water.
Treating the source of these microbes reduces or eliminates the amount of microbes entrained by passing air microbes. As these microbes can persist on the WSE as well as the water reservoir, treatment of the WSE is critical because it can serve as a continuous source of microbes for the water reservoir. Hence, treatment of the WSE should be performed at a minimum, and a coordinated treatment of the WSE and water reservoir would be optimum. The treatment of the WSE and water reservoir can be performed in one step if compounds having suitable dissolution properties are chosen and the treatment of the condensing water or wetted surface provides for drain off of the treatment compounds to the water reservoir. After treating the WSE and the water reservoir with biocidal compounds, a slow dissolution tablet such as that described in U.S. patent application Ser. No. 09/520,006, now U.S. Pat. No. 6,303,039, should deter any further microbial growth in the water reservoir.
Metals including silver (Ag), nickel (Ni), zinc (Zn), copper (Cu), and tin (Sn) are known in the art as effective biocides. For example, Ag is effective against virus and bacteria. In particular, a concentration of about 0.02 ppm (or 20 ppb) in water is effective against Legionella pneumophilia. Cu is also an effective algaecide and in some cases a bactericide. Other metals can also be effective against different microbes to differing degrees.
Metals such as these can be used as a biocide in water soluble, insoluble or slightly soluble forms. The choice depends on the particular application involving the biocide. For example, the biocide formulations taught by copending U.S. patent application Ser. No. 09/520,006 filed Mar. 6, 2000, and now U.S. Pat. No. 6,303,039 are for slow dissolution metal salts to treat a water reservoir over an extended period of time, whereas other applications may require delivery of a higher concentration of biocide over a short period of time. In either case, it is critical that the biocide formulation account for the presence of other anions that will be present in the water. Hence, of critical importance in an aqueous biocidal metal application is the stability of the metal ions in solution.
There are many anions present in water with the potential to precipitate out metal ions, and because their availability in solution is necessary to be effective against the microbes, retention of the metals in solution is highly beneficial. If provisions are not made to ensure some level of these ions in solution, they will precipitate out negating their effect against microbes, and additional materials will need to be added costing the user more in raw materials and maintenance. One known technique to ensure that these effective compounds remain in solution where they are effective against microbes is through the use of chelating agents which have a stronger affinity toward the metal ions than do the anions present in the water. Certain chelating agents such as salicylic acid (SA) are also generally known by those skilled in the art to be biocides. For example, SA is known to be an effective fungicide. Hence, the use of chelating agents such as SA along with the metal biocides will provide dissolved and stable chelated metal ions as well as a dissolved, metal-free chelating agent that can also supplement the metal biocide.
Most WSE cleaning or disinfection products are sprays (aerosols or pump) which are used to flush the surface. Most of these disinfectants contain quaternary ammonium salts, chlorine dioxide, alcohols, ethers, or trichloroethylene. A surface flush or wash generally removes debris and certain microbes physically and serves as a short-lived biocide.
An object of the present invention is to provide a biocide spray solution containing effectively chelated biocide metals which can be applied to a WSE present in a climate control device surface to treat and then control the growth of microbes on the surface over an extended period of time.
Another object of the present invention is to provide a formulation of metal salts and chelating agents combined with viscous water-soluble compounds such as polyhydric alcohols and polymers which can be applied as a spray to produce a residue of the viscous compound with the metal salts and chelating agents dissolved or dispersed therein when some or all of the water has evaporated from the solution sprayed onto a WSE in a climate control device.
These objects have been achieved by a product in the form of a cleaning and disinfection solution to the WSE that has a two-fold effect: first, it flushes and cleans the surface xe2x80x9cshockingxe2x80x9d the microbes with biocides, and, second, a long-term effect which will provide a maintenance level of biocide which eliminates any re-growth of the microbes on the surface. The latter, as we have recognized, is possible because glycerol (a polyhydric alcohol), water-soluble polymers, or other viscosity enhancing compounds are soluble in water and can be used to increase the viscosity or xe2x80x9cstickinessxe2x80x9d of the solution. Compounds such as polymers, glycerol or other polyhydric alcohols generally have a much higher boiling point than water so if the water evaporates, remaining residue will contain dissolved or dispersed biocide salts and chelating agents. Then, as more water condenses or flows through or across the surface, the dispersed or dissolved biocide metals and chelating agents will dissolve providing disinfection to the WSE and ultimately the drain pan or water reservoir collecting excess water. The extended time for which the present invention provides for treating a WSE is thus derived from the presence of water soluble residue remaining after the surface was sprayed. The slow dissolution of these ingredients will also eventually drain off of the WSE into a water reservoir or pan, and then through the drain line. Thus, this type of spray treatment would also provide for disinfection of the reservoir or pan and drain lines over an extended period of time.
The method comprising the present invention is to combine two or more metals, one or more chelating agents, and one or more surfactants in a single formulation so that the combination potentially produces synergistic effects with regard to microbe efficacy. These synergisms can exist with multiple metals, for example, because microbes colonies typically grow and thrive synergistically. Hence, by using one or more metals in solution, it is possible to produce an unexpected efficacious biocide product which exceeds the capabilities of using only one metal biocide at the maximum concentration allowed according to EPA drinking water standards.